OBJECTIVE: To assess whether onset of rheumatoid arthritis (RA) prior to conception is associated with a delayed time to pregnancy (TTP).METHODS: The study included pregnant women from across Denmark who enrolled in the Danish National Birth Cohort between 1996 and 2002 and had planned or partly planned the cohort pregnancy. RA diagnosis was identified using the Danish National Hospital Discharge Registry. Self-reported data, including TTP, maternal age, parity, prepregnancy height and weight, maternal occupational status, smoking, and alcohol consumption, were collected using a detailed computer-assisted telephone interview at ∼16 weeks of gestation. We used logistic regression analyses as well as a complementary log regression model to examine whether TTP was influenced by RA, adjusting for the abovementioned variables.RESULTS: Overall, compared with women with no recorded RA (n=74,255), women with prevalent RA (onset prior to conception) (n=112) were slightly older (mean±SD age 30.8±4.3 years versus 29.7±4.1 years), were more likely to have been treated for infertility (9.8% versus 7.6%), and were more likely to have taken>12 months to conceive (25.0% versus 15.6%). The association between RA and TTP was borderline significant after adjusting for covariates in the regression analyses (odds ratio 1.6 [95% confidence interval 1.0-2.4]). Similar results were obtained after restricting the analyses to women who had planned the pregnancy or those who were nulliparous before the cohort pregnancy.CONCLUSION: Women with RA onset prior to conception had a slightly longer TTP compared with those who did not have RA, indicating a slight reduction in fecundity.